The present invention relates to a variable venturi-type carburetor.
A variable venturi-type carburetor has been known which comprises: a suction piston changing the cross-sectional area of a venturi portion in accordance with a change in the amount of air fed into the cylinder of the engine; a needle fixed onto the suction piston; a fuel passage extending in the axial direction of the needle so that the needle can enter into the fuel passage; a metering jet arranged in the fuel passage and cooperating with the needle; and an air bleed passage for feeding air into the fuel passage. However, in such a carburetor, water, contained in air fed from the air bleed passage into the fuel passage, freezes in the cold season, thus icing the needle. This results in a lean air-fuel mixture fed into the cylinder of the engine, thereby obstructing good engine operation. In addition, the low temperature of air fed from the air bleed passage into the fuel passage reduces the temperature of the fuel flowing within the fuel passage, thus increasing the viscosity of the fuel. This slows the flow of the fuel within the fuel passage, reducing the amount of fuel fed into the cylinder of the engine and, thus, increasing the air-fuel ratio of the air-fuel mixture fed into the cylinder of the engine over the predetermined value.